docs: def zpath(filename):
      """
      Returns an existing (zipped or unzipped) file path given the unzipped
      version. If no path exists, returns the filename unmodified.
  
      Args:
          filename: filename without zip extension
  
      Returns:
          filename with a zip extension (unless an unzipped version
          exists). If filename is not found, the same filename is returned
          unchanged.
      """
      for ext in ["", '.gz', '.GZ', '.bz2', '.BZ2', '.z', '.Z']:
          zfilename = "{}{}".format(filename, ext)
          if os.path.exists(zfilename):
              return zfilename
      return filename